CORP LTT ACFT TAKES EVASIVE ACTION WHEN SIGHTING AN ACFT ON TCASII WHILE IN THE TFC PATTERN.

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WHILE MAKING OUR R HAND DOWNWIND TO BASE TURN (CLRED FOR R HAND VISUAL APCH) I NOTICED TFC ON TCASII SCREEN; SEBOUND; OUR ALT; ON CONVERGING COURSE WITH OUR ACFT. AN IMMEDIATE CLB WAS INITIATED (I CALLED IT AND AT THE SAME TIME PULLED BACK ON YOKE). WE CLBED 200-300 FT TO AVOID SINGLE ENG VFR TFC WHICH PASSED UNDERNEATH OUR ACFT. MMU TWR NEVER CALLED THIS TFC. IN FACT; I NOTIFIED TWR THAT TFC WAS OUT THERE. TWR HAD NO IDEA TFC WAS OUT THERE. TWR WAS EITHER UNAWARE OF THIS TFC OR TFC WAS SUPPOSED TO ENTER A COMPLETELY DIFFERENT QUADRANT OF THE ARPT TFC AREA. SMALL VFR AIRPLANES LNDG MORRISTOWN WERE LNDG RWY 30 AT MMU THAT NIGHT (WE NEEDED THE LONGER RWY AND HENCE LANDED RWY 23). AT ANY RATE; IF THE SINGLE ENG VFR AIRPLANE WAS ENTERING THE PATTERN FOR RWY 30; THEN THAT ACFT SHOULD HAVE ENTERED FROM THE S (IE; L DOWNWIND TO RWY 30). ANYWAY; TWR WAS DUMBFOUNDED IN REGARDS TO US CALLING OUT THAT VFR TFC AND DIDN'T REALLY VOLUNTEER ANY ADDITIONAL INFO. THE BOTTOM LINE IS WE AVOIDED A POTENTIAL MIDAIR. PLTS: DON'T RELY TOO HEAVILY ON CTLRS. USE ALL MEANS POSSIBLE TO INCREASE YOUR SITUATIONAL AWARENESS (EG; EYES; EARS; TCASII SCREEN) WHATEVER YOU CAN TO FLY SAFE AND KEEP ANOTHER ACFT AND/OR ATC FROM RUINING YOUR DAY; CAREER; OR LIFE!! WE JUST HAD AN 'RA' AND CLBED TO AVOID ANOTHER VFR ACFT JUST 3-4 MINS PRIOR TO ENTERING THE TFC PATTERN AT MMU; THIS NIGHT. TAKE A GUESS AT WHAT THE CREW'S BLOOD PRESSURE READINGS WERE AT THIS POINT.